engine horse power

[georgepatten]

I have plans for a 27' wood tug which call for a diesel engine of 130 to 200 hp. How do I convert these figures to the appropriate steam engine hp and boiler? Thanks all

[JonRiley56]

I have been told that 1 hp will push 1,000 lbs in a steam set up..............if you have an idea of how much your tug will weigh it might give you a starting point

jon

[fredrosse]

In fact there is no difference, a horsepower is a horsepower, be it steam, or an IC engine, or a horse!

Horsepower is the rate of doing work, and defined as 550 ft-pounds of work output per second, or 33,000 ft-pounds of work output per minute. Work is defined as a force applied through a distance.

This can be with a high speed engine with low torque, or a low speed engine with high torque, either way the power output is defined the same.

The relevant parameters defining engine horsepower is shaft torque (T), and rotational speed (RPM). The torque here is the average torque produced by the engine, not the maximum torque for design of the connecting rod and bearings, etc., which is often several times greater than the average torque.

If the torque produced by applying a force to a lever (attached to the shaft), say an applied tangential force of 1 pound, with a 1 foot long lever arm, the torque is one pound-foot. However the work done in one revolution of the shaft is actually a movement of 6.28 feet, (2 x Pi x Radius), so in one revolution this condition produces 6.28 ft-pounds work. The equation relating engine torque and RPM then is:

HP = RPM * Torque (pound-ft) * ( 2 Pi ) / 33,000

Enough of the formulas, but with a well sized propeller, you can get to hull speed, (about 1.3 x the square root of the boat's waterline length) with about 1.5 to 2.0 horsepower per ton of displacement.

[fredrosse]

Unless the "Tug" is actually going to push big barges around, or help docking ships, the numbers for quoted horsepower are far far too much. If your hull weighs 3 or 4 tons, then 5 to 10 real horsepower would be plenty to reach hull speed. Speed much beyond that, on a displacement hull, would not be practical. You do however need the right propeller, that means a big, slow turning propeller. Do you have any details as to the boat's lines, displacement, photographs?

Go on youtube and look up "Oberon on Windemere", see what a real 15 horsepower steam engine can do on a 28 foot fast launch.

[fredrosse]

I would think the Mosquito Enterprises machinery would be a good fit to your steamer. The 55 square foot VFT boiler they sell can easily make enough steam to produce 5 or 6 real horsepower, and if that boiler is forced with a brisk fire 10 or more continuous horsepower would be available. The Mosquito Enterprises tamden compound engine looks about right for your tug also.

Do you have any data as to hull and displacement?

[artemis]

I would think the Mosquito Enterprises machinery would be a good fit to your steamer. The 55 square foot VFT boiler they sell can easily make enough steam to produce 5 or 6 real horsepower, and if that boiler is forced with a brisk fire 10 or more continuous horsepower would be available. The Mosquito Enterprises tamden compound engine looks about right for your tug also.

Do you have any data as to hull and displacement?

I do the website for Mosquito Enterprises - and have seen both the VFT55 and the Compound Engine in operation. The boiler meets code and will probably power a 10+HP engine. The engine will "shove" (you should see the bow wave) the Mosquito hull at about 7+ knots (there's always competition between various members of the NWSS as to speed and Mosquito is usually a part of it - some times he wins and sometimes he loses, but 7+ knots is plenty good. It's not the MPH it's the "fun-per-mile"

[georgepatten]

attachment shows a 27 foot tug with a displacement of 10600 lbs, dead weight not known. according to the waterline formula it has a hull speed of about 6.25 knots. Can anyone give me an idea of what HP steam engine and size boiler I'm looking at? Sure like to get this nailed down as close as possible any advice helps. Thanks, George

[Mike Rometer]

Nice profile on that George! Looks the Biz.

[georgepatten]

Thanks Mike, looking forward to getting this project moving.

[DetroiTug]

Hi George,

For just general cruising, I would go for around 6-8 horsepower.

The horsepower comes from the boiler, so for that amount of power out of a VFT, about 60 sq ft of heating surface. More or equal to that for wood or coal, a little less for oil or propane. The engine? Run a small engine fast or big engine slow for the same net torque. I would also suggest a twin. The tug I have now has one and I really like it. 3+3X4, that would be plenty for yours. Whichever way you go on the boiler and engine, it will work, even a smaller 3X4 single and 30 sq ft VFT will push it, it just won't get near hull speed. And then again - it might.

Engine horsepower ratings are a bit ambiguous. My buddy has a steambike (Tony Grzyb on http://youtu.be/piv_P7AiKUY ), he has a 1/4 hp rated Strelinger coke bottle engine on it. However, with it's boiler and the RPM he runs it at, it puts out more than 3 hp.

How are you planning to arrange the engine and boiler?

-Ron